Anhydrous hydrogen bromide is widely used as an intermediate in the chemical industry. It is utilized in the production of inorganic bromides by reaction with metal hydroxides, oxides, or carbonates; in the production of organic bromides by reaction with alkyl alcohols or alkenes; and as a catalyst for oxidations, alkylations, and condensations in organic chemistry. Sodium bisulfate is likewise widely used in textiles and chemical processing and as a preservative.
The production of hydrogen bromide from sodium bromide is known. The reaction typically includes adding sulfuric acid to sodium bromide and water according to equation (I):

One drawback of known production methods for producing anhydrous hydrogen bromide is that a high boiling water/HBr azeotrope stream is produced. The azeotrope is difficult and expensive to purify as will be appreciated by one of skill in the art.
U.S. Pat. No. 1,379,731 to Theimer, describes a method to produce a stream of 48% HBr/water azeotrope of aqueous hydrogen bromide. This azeotropic solution has only limited commercial application due to the presence of the water. One approach to converting this azeotropic stream of 48% hydrogen bromide to anhydrous hydrogen bromide is to utilize pressure swing distillation where one column at high pressure will produce an aqueous stream of hydrogen bromide greater than 48%. A second column at lower pressure will produce a stream of hydrogen bromide with a concentration of less than 48%. Such a system will effectively break the azeotrope and produce an essentially anhydrous stream of hydrogen bromide; however pressure swing distillation requires the distillation of acidic aqueous streams under high pressure. This process will have high costs for two reasons. First, the process must be carried out in equipment designed to withstand the high pressures and corrosive environment. Second, energy costs are high due to the high reflux ratios required to affect the distillation process as well as the high heats of evaporation of aqueous systems.
U.S. Pat. No. 2,705,670 to Chao also discloses a continuous process for producing HBr from sodium bromide; however, that continuous process produces amounts of molecular bromine (Br2) and sulfur dioxide which range from about 0.035% to about 1% or more. Indeed, Applicants have observed that duplication of the process in Chou results in excessive amounts of bromine. The '670 patent also contains what appear to be batchwise examples, but does not address handling of the HBr azeotrope or purification of bisulfate salt; features critical to the commercial usefulness of the present invention.
The production of unwanted bromine and sulfur dioxide is believed due to the fact that sulfuric acid reacts with HBr to form the undesirable products in accordance with equation II:2HBr+H2SO4 →Br2+SO2+2H2O  IIwhen the salt is added to aqueous reactants as described in the reference. The present Applicants have also noticed that the unwanted production of bromine can occur due to the presence of bromates in the NaBr feed.
The need for a high-yield, environmentally friendly process to anhydrous hydrogen bromide utilizing salts is seen by the fact that large producers of bromide salt streams recycle them through bromine suppliers. For example, in St. Louis, Mo. a large chemical manufacturer produces 150 million pounds of a 44% NaBr solution. To convert this to a usable reagent they must ship it to Great Lakes Chemical in Eldorado, Ark. for reprocessing through conventional chlorination routes (see U.S. Pat. Nos. 2,143,223 and 2,359,221).
The present invention is directed generally to an improved high-yield slurry process which produces both anhydrous hydrogen bromide and low-bromide bisulfate salt from a bromide salt source. In the inventive process, bromide salt reacts with sulfuric acid to produce crude HBr and crude bisulfate salt. The crude HBr stream contains water and may also contain a small amount of bromine. The crude bisulfate salt contains some bromide. The crude HBR and crude bisulfate are processed into anhydrous HBr and purified bisulfate, respectively.
Co-production of the two products minimizes waste and enables economical re-processing of bromide salt streams. The process is also capable of being run batchwise which allows for processing of a variety of starting materials and allows for re-processing of the azeotrope as will be seen in the examples appearing hereinafter. In certain circumstances it may be necessary to reduce the minor amounts of bromine that accumulate in the process. This can arise, for example, when bromates are present in the bromide salt feed. Bromine is an undesirable component in the system because it is a highly reactive impurity. Also, due to the presence of bromide in the bisulfate product, there exists a need in the process to purify the bisulfate salt in a cost-effective manner.